Aquaveo & Water Resources Engineering News

Does your SRH-2D project have a box culvert or pressure zone with overtopping that is proving to be a bit difficult to get correct?

Box culverts or pressure zones with overtopping are common features added to many SRH-2D models. Depending on how the pressure zone is created in your Surface-water Modeling System (SMS) project, this can be a tricky process for SRH-2D to handle. Here are some steps and tips for creating this feature successfully in SMS.

1 Use Quadrilateral Elements

Create quadrilateral elements between the boundaries of the pressure zone. Using quadrilateral elements tends to increase the stability and reliability of the SRH-2D model run. Quadrilateral elements can be created in one of two ways.

The first is to create the quadrilateral elements when creating the 2D mesh. Create a polygon for the area between and around the pressure zone. Assign this polygon with the Patch mesh type in the 2D Mesh Polygon Properties dialog.

The second method is to create the quadrilateral elements directly in the mesh using the Split/Merge tool and the Switch Element tool. This can be time-consuming, so it is only recommended for small adjustments.

2 Create Voids

Create voids in the mesh on either side of the pressure zone. There are two options for creating these voids, but one option seems to work better.

The first option, and the more stable one, is to create the voids on either side of the pressure zone when generating the mesh. Create the voids as polygons and assign them the None mesh type. It is generally best to make each void a quadrilateral polygon to imitate the thickness of a concrete wall or barrier.

The second option is to generate the mesh then use the Select Elements tool to select and delete the elements where the voids should be. Using this method requires renumbering the mesh nodes. There is a risk that you will not be able to delete all of the nodes related to the elements which can make your mesh unusable to SRH-2D.

3 Assign Boundary Conditions

Two arcs are needed to define the pressure zone. Each arc should be created on an SRH-2D boundary condition coverage. When creating the arcs, make certain all 2D mesh elements between the arcs are quadrilateral elements. Also, it is advisable to have at least one row of quadrilateral elements just past the downstream arc.

Once the arcs have been drawn, select both arcs and open the SRH-2D Linear BC dialog. Set both arcs to the Pressure type, making sure the correct arc ID is assigned to upstream versus downstream, and turn on the Overtopping option.

Both the boundary condition coverage and the 2D mesh can be added to your SRH-2D simulation to have a pressure zone with overtopping included in the results.

Try out adding a pressure zone in SMS today!

This post was originally published September 12, 2018.

The Groundwater Modeling System (GMS) contains many tools for visualizing data. The contour visualization tools are particularly helpful in viewing solution data. With contours, GMS provides several options for how contours will be displayed, including options for the contour legend. When a legend is added to the contour display, it is not always clear what the units of the values shown in the legend are. With GMS 10.8 improvement to the Contour Legend Options allow displaying the data units with the legend.

The Contour Legend Options dialog is available for the contour dataset displayed in the Graphics Window. Accessed from the Legend Options button on the Contour Options dialog, the Contour Legend Options dialog controls the formatting and location of a displayed legend. The tool is only available if the Legend check box on the Contour Display Options Dialog is checked. This dialog includes formatting options such as a title field, a font selection button, as well as fields for height and width. Furthermore, the dialog offers location options that includes a combo box for specifying the location of the displayed legend. Visit our wiki page to view descriptions of each feature this dialog provides.

Here is a step-by-step of how to execute this feature:

1. Select Contour Options.
2. At the bottom of the Dataset Contour Options dialog, ensure that the Legend option is checked.
3. Select Options in the Legend section.
4. In the Formatting Section of the Contour Legend Options dialog, enter the respective unit keyword: "UNITS" for DS (Datasets) and "TUNITS" for (Time steps).

The ability to add the unit type to the legend is a user requested feature that helps make presenting data clearer for your audience. This and other improvements are continuously being added to GMS. Head over to GMS and check out the options for legend displays and other features.

If you need to make a change to a mesh, should you use the toold in the 2D Mesh module to edit, or instead regenerate the mesh? A 2D mesh consists of elements that define the computational domain of the numerical model. A numerical simulation requires a geometric definition of its domain– the mesh, available for use in SMS 13.3. Occasionally when constructing a mesh, a moment occurs where the mesh is insufficient for any reason.

In most cases the recommendation is to regenerate the mesh; as opposed to editing the mesh manually. The following list involves common circumstances where one may manually edit a mesh:

• There is no mesh generator coverage present.
• Deleting Outer Elements: Since the triangulation process creates elements (i.e. thin triangles) outside the mesh boundaries, deleting outer elements provides some refinement.
• Merging Triangles/Element: Numeric solvers are more stable and accurate when quadrilateral elements are rectangular and triangular elements are equilateral.
• Editing Individual Elements: After compound edits, a mesh could benefit from individual manipulation to increase stability. Swapping edges: Think of the two triangles as a quadrilateral, and the common edge between them is a diagonal of the quadrilateral. By swapping this common edge, it changes to be along the opposite diagonal of the quadrilateral. If this edge is clicked again, it returns back to its original state.
• Turning a specific element into a void element.

You may make edits in the Mesh Generator coverage. Manual edits should be intentional and reserved for small sections of a mesh. Generally, manual edits of a mesh ought to be minimal.

In nearly all cases the recommendation is to regenerate the mesh; as opposed to editing the mesh manually. This is because any process that edits a mesh, causes the node and element ordering to become disorganized. Additionally, editing a mesh invalidates any solution files that have been previously saved. Manually editing a 2D mesh risks creating issues with the assigned elevation data or other datasets being used. As such, if there is a solution dataset attached to the mesh, the model simulation should be re-run.

A useful tip is reviewing your mesh before generating, using the preview tools that are available in a given dialog. Make adjustments to the arcs, vertices, and polygons on the mesh. Do not be afraid to add more arcs, vertices, or polygons if further refinement is needed.

If you want to generate a new mesh with the desired edits, you will need to create a mesh generator coverage. The following are examples of tools that can create a new mesh:

• Map → 2D Mesh tool.
• 2D Mesh from 2D Grid in the toolbox.
• Additionally, most of the Unstructured Grid tools may be utilized to generate a new mesh.

Make use of the mesh editing and generating capabilities of SMS 13.3 today!

The Surface-water Modeling System (SMS) continues to expand its capabilities. Currently, SMS is expanding to make more use of unstructured grids. An unstructured grid (UGrid) is a flexible geometric object that can include cells such as 2D and 3D cells with any number of faces and nodes. This flexibility allows for more realistic modeling of geological features.

In SMS, UGrids can be imported directly or created by converting an existing geometry such as a 2D mesh, 2D scatter set, Quadtree or map feature objects. When creating an UGrid from an existing geometry, it is usually best to make certain the geometry already refined to the level you need for your project. However, sometimes the Ugrid needs to be refined after it has been generated or imported. To do this, SMS provides two tools for refining UGrids: Refine UGrid and Refine UGrid by Error.

Both tools are located in the SMS Toolbox under the Unstructured Grids folder.

The Refine Ugrid uses an existing UGrid then splits (refines) the elements into smaller elements. The Refine UGrid tool provides you with the option to select datasets with “locked” nodes—any node with a non-zero scalar value. Any cell edges that contain one or more locked nodes will not be split. Utilizing such a tool will equip you to complete a surface-water modeling project with focused accuracy and efficiency. .

Similar to the Refine UGrid tool, the Refine UGrid by Error tool produces a 2D UGrid that has been refined as a result of an existing 2D UGrid, however this tool integrates elevation rasters into the process. Entering a value that guides the acceptable error threshold, the maximum number of iterations to perform, and the necessary elevation rasters are all required components of the input parameters for this tool.

Being able to refine UGrids adds increased accuracy for your surface-water projects in SMS. Check out the refine UGrid tools in SMS today!